This is by far the best historical book I've been able to find on the topic of German destroyers of WWII. Better than the Koop book and others.
It is not an in-depth naval analysis, nor is it a technical, illustrated guide. So, naval engineers and modelers will perhaps feel a little disappointed in this book.
Whitley covers the different types pretty well, there is an attempt to technically describe their armament (chapter 4) but comes as a rather feeble attempt, there are some plans with enough detail of Z-15, a type 34A. However, the descriptions of the power plants and other equipment such as radios/radar is very, very good, as is the chapter on weapons directors and their development.
Germany's torpedo boats would have been classified as destroyers based on displacement and range in most other navies, so they are included too, with equal coverage (Wolf class, type 23/24/35 etc), with type 41 getting the lion's share (including decent plans). One word about the plans given here: they are no match for more recent material, specially that coming from Polish publishers like Kagero and AJ Press, so keep that in mind if that is what you are after.
The photographs chosen are clear, large in size, but not enough in number. You could supplement -as I did, with the small, but much better illustrated Paul Beaver work titled German Destroyers and Escorts (ISBN 089404060X). The ones that are included are gorgeous, most of them not published elsewhere, that I know of, such as the ones taken by the british when the Kriegsmarine surrendered at the end of the war. Plenty of structural detail, but you never get rid of the feeling of wishing for more...
The historical narrative is where this book shines like a diamond. It made for riveting reading. For me, it is a keeper.